This section provides background information related to the present disclosure which is not necessarily prior art.
A hydraulic piston mechanism is provided in an automatic shift gear of a vehicle such as a car in order to switch between connection and disconnection of a clutch to turn on and off the transmission of a torque. The piston mechanism is provided with a canceller for cancelling a centrifugal hydraulic pressure exerted on a piston during rotation.
FIG. 3 illustrates an example of an inner mechanism of an automatic shift gear including this type of piston mechanism. A canceller 52, a piston 53, a return spring 54, and the like are assembled in a housing 51 configured with a rotation drum or the like. A pressure chamber 55 is formed between the housing 51 and the piston 53, and an operating oil is supplied to the pressure chamber 55 such that the piston 53 reciprocally moves to press and connect the clutch 56. A centrifugal canceller chamber 57 is formed between the piston 53 and the canceller 52, and an operating oil is supplied to the centrifugal canceller chamber 57 such that a centrifugal hydraulic pressure exerted on the piston 53 during rotation is cancelled.
In addition, an opponent member 58 configured with a pinion shaft or a carrier of a planetary gear mechanism is disposed opposite to the centrifugal canceller chamber 57 in the canceller 52, and an oil path 59 for supplying an operating oil to nearby components as a lubricating oil is formed between the canceller 52 and the opponent member 58.
An outer circumferential seal unit 60 configured with a lip seal is provided on an outer circumferential portion of the canceller 52 and comes into contact with the piston 53 to seal an operating oil supplied to the centrifugal canceller chamber 57. In addition, a second outer circumferential seal unit 61 configured with a lip seal is provided on the outer circumferential portion of the same canceller 52 and comes into contact with the opponent member 58 to seal an operating oil (lubricating oil) flowing through the oil path 59.
In the piston mechanism having the above-mentioned configuration, since the centrifugal hydraulic pressure exerted on the piston 53 during rotation is cancelled, the piston 53 can be properly operated. In addition, since the operating oil (lubricating oil) is supplied from the oil path 59, the nearby components can be properly operated. However, in the seal structure, since the second outer circumferential seal unit 61 which comes into contact with the opponent member 58 has an end face seal shape in which the lip of the second outer circumferential seal unit 61 comes into contact with an axial end face of the opponent member 58, there are problems as follows.
(1) When an axial movement of the opponent member 58 is large, it is difficult to ensure traceability of the lip.
(2) Although the second outer circumferential seal unit 61 needs pressure resistance due to the centrifugal hydraulic pressure exerted thereto, since margins have to be set to be great and pressure resistance has to be ensured, a cross-section of the lip has to be great. Therefore, stiffness of the lip increases, and a reaction force increases, so that operability thereof may be degraded.
(3) Due to the centrifugal hydraulic pressure, there is a possibility that turn-up of the lip may occur. [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-278798 (FIG. 3).